The present invention relates to a dust seal in a scroll fluid machine such as a scroll compressor, a scroll vacuum pump, a scroll expander or a scroll blower.
A scroll fluid machine comprises a stationary scroll and an orbiting scroll which can be revolved around an eccentric axial portion of a drive shaft. A stationary wrap of the stationary scroll engages with an orbiting wrap of the orbiting scroll to form a sealed chamber between the stationary and orbiting scrolls. By rotating the drive shaft, the orbiting scroll is eccentrically revolved with respect to the stationary scroll so that a gas sucked through the outer circumference is compressed toward a center. To prevent leakage through the outer circumference of the scroll or to prevent dust from coming in from the outside, an annular dust seal is provided between the stationary and orbiting scrolls.
In FIG. 10, a dust seal is shown as 25. On a contact surface of between stationary and orbiting portions, there is formed an annular groove 24 in which a sliding member 27 is provided on a backup tube 26.
A stationary scroll 17 has an inlet 15 on the outer circumference and an outlet 16 at the center. A spiral stationary wrap 16 of the stationary scroll 17 engages with a spiral orbiting wrap 22 of an orbiting scroll 21 eccentrically revolved around an eccentric axial portion 20 of a drive shaft 19. An annular groove 24 is formed on the front surface of a stationary end plate 23 of the stationary scroll 17, and the dust seal 25 engages in the annular groove 24 to prevent a gas from leaking and dust from invading.
In FIG. 11, the dust seal 25 comprises the sliding member 27 and the backup tube 26 in the annular groove 24. The sliding member 27 is made of low-friction, heat-resistant, wear-resistant self-lubricating synthetic resin such as “Teflon”™ or metal. Its section is generally rectangular.
The backup tube 26 comprises a ring made of elastic sealing material such as silicone rubber or fluorine rubber.
In the backup tube made of silicone rubber, chemical resistance is low, while in the backup tube made of fluorine rubber, chemical resistance is high but it manufacture is difficult.
Even if the backup tube is made of any of the materials, repulsive force decreases with time, so that pressing force by the sliding member 27 decreases.